FIGS. 7 and 8 depict a conventional key input device 101 for an electronic equipment 100, wherein an upper casing 102 cooperates with a lower casing 103 to form a receiving chamber 104. The receiving chamber 104 is divided into three small chambers 107, 108 and 109 by upper and lower printed circuit boards 105 and 106 arranged in the receiving chamber 104 and fixed to and supported by the upper and lower casings 102 and 103, respectively. A plurality of keytop switches 114, each having a keytop 110, a key case 111 and electrode pins 112 and 113, are disposed on the printed circuit board 105. The small chamber 107 is nearly occupied by the key cases 111. The pins 112 and 113 are inserted into through-holes (not shown) in the printed circuit board 105 and fixed thereto by soldering or the like. The pins 112 and 113 are electrically connected through a contact electrode portion (not shown) in the key case 111 when the keytop 110 is depressed in the direction of an arrow A (FIG. 8). This kind of keyswitch (although having four pins) is disclosed in detail in Japanese Patent Unexamined Publication No. 55-143720, for example. As shown in FIG. 8, a spring 115 serves to bias the keytop 110 in the direction of an arrow B, and printed conductors or wiring strips 116, formed on a lower surface 117 of the printed circuit board 105, serve to connect the electrode pins 112 and 113 of the keyswitches 114 to an external circuit, power source or the like. On the other hand, circuit elements or electronic parts or components 118 such as, for example, integrated circuits are mounted on the printed circuit board 106. Pins 119 of the electronic components 118 are inserted into through-holes (not shown) in the printed circuit board 106 and fixed thereto by soldering or the like. Printed conductors or wiring strips 120, formed on a lower surface 121 of the printed circuit board 106, serve to connect the electrode pins 119 of a plurality of electronic components 118 to each other or to an external circuit, power source or the like. Connectors 122 and connecting cables 123 serve to connect the two printed circuit boards 105 and 106 to each other with the circuit boards 105, 106 having a space therebetween.
In this kind of conventional key input device 101, however, the key cases 111 occupying the small chamber 107 nearly cover an upper surface 124 (FIG. 7) of the printed circuit board 105 so that it is impossible, in practice to form printed conductors or wiring strips on the upper surface 124. Furthermore, the electrode pins 112 and 113 extending downwardly from the key cases 111 project out from the lower surface 117 of the printed circuit board 105 and the printed wiring conductors or strips 116 are formed on the lower surface 117 for establishing electrical connection to the electrode pins 112 and 113 through the solder or the like. Therefore, it is difficult, in practice, to mount the electronic components 118 with associated pins 119 on a lower surface 117 of the printed circuit board 105. Consequently, since it is necessary to provide another printed circuit board 106 in order to mount the electronic components 118, there is a limit in size- and weight-reduction of the key input device 101. In other words, it is difficult to increase the mounting capacity of the electronic components 118 and, hence, to enhance the function of the drive within a limited occupation space. In addition, the key input device 101 requires at least two sets of connectors 122 for the purpose of connecting the printed circuit board 105 on which the keyswitches 114 are mounted to the printed circuit board 106 on which the electronic components 118 associated with the keyswitches 114 are mounted.
There has also been proposed a switch structure in Japanese Patent Unexamined Publication No. 1-276520, which aims at reduction of the number of components and simplification of the structure. A switch assembly 131 of this proposal comprises, as shown in FIG. 9, a rigid dielectric substrate 135 formed on an upper surface 134 thereof with printed conductor or wiring strips 132 and 133 constituting an input conduction path and an output conduction path, respectively. A spring band or strip 139 is fixed to the output conduction path 133 at stationary contacts 137 at the lower ends of four elastic leg portions 136 thereof and has two movable contacts 138 at intermediate portions thereof, a switch head 142 having a projecting portion 141, is fitted in a hole 140 of the spring band 139 and serves to bring the movable contacts 138 of the spring band 139 into contact with the input conduction path 132 when depressed in the direction of an arrow C. An input lead piece 147 and an output lead piece 148 has ends 143 and 144 thereof respectively connected with the input conduction path 132 and the output conduction path 133 and the opposite ends 145 and 145 extending downwardly. A stop 149 restricts the head 142 from being depressed in the direction C beyond a fixed depth.
Japanese Patent Unexamined Publication No. 1-276520 does not disclose the manner of mounting the switch assembly 131, however, it is considered from the arrangement and shape of the input and output lead pieces 147 and 148 that the switch assembly 131 is also mounted by inserting the input and output lead pieces 147 and 148 into through-holes in a printed circuit board. Accordingly, even if the switch assembly 131 is applied to the key input device, it is necessary to provide another printed circuit board for mounting electronic components as with the key input device of FIGS. 7 and 8.